Underground integrally-formed pile column type bridge pier construction method

The invention discloses an underground integrally-formed pile column type bridge pier construction method. The method comprises the steps that a stand column segment is subjected to hole drilling at the position of a bridge site in the first place, a stand column steel casing is placed, and a dry hole and the reserved gap in the outer side of the downwards-placed stand column steel casing are filled with mortar; after stand column construction is finished, hole drilling of pile foundation segments is performed, reinforcing cages of pile foundations and a stand column are placed, overall one-time pouring of concrete is performed on the reinforcing cages of the pile foundations and the stand column, and one-time underground forming of the stand column and the pile foundations is completed; after one-time underground forming construction of the pile foundations and the stand column is finished, after pile testing is qualified, construction of other lower portions and upper portions is performed till the train-pa